Bats have been duking it out with the virus that causes Middle East respiratory syndrome, or MERS, for a long time, a new study suggests.

The MERS virus grabs hold of the DPP4 protein on mammalian cells to gain entry into them. Bats have more changes to their DPP4 proteins than other animals do, Jie Cui of the University of Sydney and colleagues report October 10 in Virology Journal.

Many of those changes would loosen the virus’s grip on its favorite handholds, indicating that the bats and the virus have engaged in a long-term evolutionary arms race with the virus finding new ways to grasp the protein and the bats prying it off again.

The study is further evidence that the MERS virus, like its cousin SARS, first evolved in bats before making the leap to humans and other possible intermediate hosts, such as camels.